the two other surviving presidents, george bush and george w. bush were all -- were unable to attend. president obama began addressing the crowd a few moments ago. >> we rightly and best remember dr. king's soaring oratory that they. how he gave a mighty voice to the quiet hopes of millions, how he offered a celebration path -- salvation path. his words along to the ages. investing a power and prophecy unmatched in our times. >> our correspondent is in washington at the celebrations. can you give us a flavor of the atmosphere there today? >> it is a very special atmosphere. tens of thousand of people turned up in spite of the bad weather. john lewis, the only man, civil rights activist, who stood here 50 years ago with mart luther king. we had actors, jamie foxx and oprah winfrey spoke. all very well receed from this ry mixed crowd, but as you can imagine, the stars here were the three presidents. you don't get to see three presidents speaking in the space of 45 minutes that often and the biggest of them all, we can still see behind me the first